In blast furnace operation, it is common practice to preheat incoming air for the blast furnace, by passing the air through a heated checkerwork of checker tiles in a large regenerative stove. The checker tiles in the stove have gas passages to allow hot gases leaving the blast furnace to flow through the checkerwork and heat the checkerwork by transfer of heat from the hot gases to the tiles, and later to allow air that passes to the blast furnace to pass through the checkerwork and to be heated by transfer of heat to the air from the thus previously heated checker tiles.
For optimum results in such service, the checker tiles should be so shaped that they can be readily assembled into the checkerwork by being fitted together with laterally and vertically adjacent tiles, and with supporting means below tiles in the lowermost layer of tiles in the checkerwork. Moreover, the tiles should be such that after assembly in the checkerwork they are securely located relative to the adjacent tiles of the checkerwork that abut their sides and their top and bottom ends.
After assembly into the checkerwork, the tiles should provide passages through the checkerwork through which passages hot gases and air can alternately pass without excessive pressure drop which could be damaging or dangerous to the shell or other structure of the large stoves, and which passages provide large heat transfer areas.
Since transfer of heat to and from checker tiles and operation of the stove causes the tiles to change dimensions due to thermal expansion and contraction, the tiles should be so supported relative to each other and to the supporting means for the checkerwork that relative movements between the tiles and between the tiles and supporting means is permitted to allow for such changes in dimensions of the tiles without damage to the tiles or supporting means.
Furthermore, the supporting means at the bottom of the stove supporting the checkerwork of checker tiles must be such as to permit relative movements between the supporting means and the tiles between the supporting means and supporting columns or other fixed supports to allow for movements arising from expansion and contraction of the tiles and supporting means during heating and cooling of the supporting means and the checkerwork supported by it.
The checker tiles should be strong enough, and have securing means as to permit the tiles to be assembled into a checkerwork without crushing of the tiles. The tiles must also be strong enough to withstand the weight of tiles above them in the checkerwork under high temperatures and changes in temperatures, and to withstand degradation due to the movement of hot gases and the action of gas-laden impurities.
Failure of checker tiles in the checkerwork can cause checker tiles above the failure location to collapse, thereby destroying a substantial portion if not all of the checkerwork. Crushed or damaged checker tiles can pile up and cause clogging of gas passages and excessive gas pressure drop. In such cases, the stove must be taken out of service and the collapsed checkerwork removed and new checkerwork prepared and installed. It is important therefore that the checker tiles and checkerwork built of them be able to resist failure under the severe conditions of use, and to be readily removed and replaced if failure does occur for any reason.
Moreover, it is desirable that the checker tiles be of such shape that they can perform the above indicated functions and yet be manufactured without excessive cost as because of molding problems or waste of material.
It is an object of the invention to provide checker tiles and supporting means that can provide all or as many as desired of the above indicated desirable features, and which can avoid most or all of the problems indicated above.